Silver halide emulsions containing antifogging agents



Patented Sept. 4, 1951 SILVER HALIDE EMULSIONS CONTAINING AN TIFOGGING AGENTS Douglas James Fry, Ilford, England, assignor to Ilford Limited, Ilford, England, a British com- No Drawing. Application November 17, 1949, Se-

Great Britain November,

rial No. 128,025. In

3 Claims. 1

comprising a light-sensitive gelatino silver halide emulsion.

It is well known that light-sensitive gelatino silver halide emulsions tend to yield, on development, a deposit of silver even in those areas which have not been exposed to light. This, more or less uniform, deposit is generally referred to as chemical fog and is disadvantageous in degrading the high-lights of the developed negative or print. The tendency to the formation of fog is increased on keeping the emulsion, sothat photographic materials which have been stored for a long time, especially in humid conditions, generally show a high fog density. The tendency to the formation of fog is also increased by development at high temperature, e. g. in tropical conditions. Photographic gelatino silver-halide emulsions may be stabilised against the changes which-give rise to fog, and the general level of fo may be reduced, by adding to the emulsions various organic compounds. Such additions, however, frequently adversely affect the other sensitometric characteristics of the emulsions, e. g. the speed and contrast characteristics of the emulsions.

According to the present invention gelatino silver halide photographic emulsions contain a small quantity of a compound of the general formula:

droxy or carbalkoxy group, and R2 is a hydrogen atom or an alkyl, aralkyl, aryl, alicyclic or heterocyclic group, or R1 .and R2 together form the residue of a ring linking the 5- and fi-positions. Such emulsions show a much reduced tendency to develop fog, but their sensitometric characteristics are otherwise very little affected by the added compounds.

Compounds of the foregoing general formula may be obtained by reacting 2:5-diamino-1z3z4- triazole (also known as guanazole) with a {3- ketonic ester, a cyclic fi-keto ester, or a malonic or cyanacetic ester. fi-Ketonic esters yield var-- iously substituted compounds according to the particular p-ketonic ester employed. A'suitable fl-ketonic ester is acetoacetic ester and a suitable cyclic p-keto ester is ethyl-cyclohexanone 2- carboxylate. Cyclic p-keto esters produce substances in which R1 and R2 jointly form the residue of an alicyclic ring linking the 5- and 6-positions.

The general formula assigned to the products of these processes is believed to be correct and follows the general lines of the structure for other compounds of similar type referred to in Bellsteins Handbuch der Organische Chemie, volume XXVI, page 4117. However, it is to be understood that the compounds employed in the present invention are the compounds obtained by the processes outlined above whatever their chemical structure may ultimately prove to be.

The following are examples of the production of typical compounds for use in the present invention:

Example 1 1 gm. 2z5-diamino-lz3:4-triazole (1 mol.) is mixed with 1.3 gm. ethylacetoacetate (1 mol.) in 5 cc. glacial acetic acid and the mixture boiled. The reactants first dissolve, and the product then quickly separates. After one hour the mixture is cooled and the product isolated by filtration. It may be purified by crystallising from water. The melting point is above 290 C. Ethyl alcohol may be used as solvent in place of acetic acid and excess ethylacetoacetate up to a total of 5 mols. gives the same product.

This particular productis believed to have the formula:

Eaample 2 a reflux condenser for three hours; solid is precipitated during the heating. It is isolated filtration and recrystallised from aceticacid. Pi; above 285 C. V

This product is believed "to h'ewe "the if'o'rmula;

Example 4 2.0 gm. "2:5 -diamino -1::3z-4 triazole is 'mixed with 3.4 gm. ethyl cyclohexanone carboxylate in 15 cc. glacial acetic acid and the whole heated under a reflux condenser for-on'efhour; solid precipitates almost immediately heating begins. After cooling it is collected and recrystallised from water, M. Pt. about 340". The-same 'com- H pound "is obtained when the two reactants are heated in an alcoholic solution of sodium ethox- "ide prepared from Q' i'G gm sodium-and 15 coalcohol, followed by acidification to precipitate the product. p This compound is believed "to have the formula:

CH2 be c FT-1N L .O .NE. H2 N on: N

Example -5 This is preparedas in Example iby heating 1.0 gm. 2:5-diaminotriazole and'2.2 gm. ethyl benzylacetoaoetate in'510 cc. glacial'acetic acid. "The product is precipitated during the heating-period. After recrystallisation from water it melted above 295 C.

This compound is believed to have mula:

the for- Example 6 Prepared as in Example -1 "byheating '1.0-gm.

2:5-diaminotriazole and 1.8 gm. ethyl a-furoylacetate in 5.0 cc. glacial acetic acid. Theproduct was recrystallised from aqueous acetic acid "and melted above 305 C.

This compound 'is believed tohave the forp the control increased considerablyzon .keepin 'at men:

Example 8 1.0 gm. '2:5-d1am ino-1:'3i4-triazo1e is mixed with '2124 pm. ethyl 'cyciopentanone 2m dicar 'boxylate 8 cc. 'glaciala'cetic acid and 'theunixture boiled for 1 hour. The product was' collected and crystallised from glacial acetic acid and then melted at'305" 'C.

This compound is believed to have the formula:

[Only very small quantities of the-compounds are necessary to stabilise the emulsionsagainst the development of fog. For examplearange of qu'antitiesof-QO'Z g. to 1 g. v'foranemulsion con taining 11/2 g. :mols. silver iodobromide is usually suflicient.

f'L hus, Z'for.examp1e,;0.5 g. .ofthecompounds .ob= tained by the processes of Examples 1 and 4 were added (dissolvedin Water, dilute caustic soda or ethyl alcohol.) to .an emulsion containing 1 /2 .3. mols. of silver .iodo'bromide, andthe emulsion .Was then coated on a support. A control coating was made with emulsion not containing the said compound. Specimens of the control and test emulsions were tested. for fee density and speed after storage for 8 days underino'rmal conditions (normal keeping); Further specimens were stored in a sealed container for 8:.days at 120 F.

The following table shows :the results obtained:

Normal Keeping I .8'Days iiti2( l'..

.Fog 1 Relative Fog Relative "density lo speed density logspeed It-will 'bezseen that whereas the fog density of F.,"that.of the test specimens did not,a nd that .the speed of the emulsion -was nod-seriously afieeted. r v

The compounds i-OfzQfiCh of Examples-2, 3,;5,1.8,

' '7 and Bumay the similarly .-,employed with dike .effect.

.W a iI;s .m ;-1 o l 1. A photographic gelatino silver halide emul- 5 sion containing a small quantity of a compound of the general formula:

where R1 is selected from the class consisting of alkyl, aryl, aralkyl, alicyclic, heterocycllc, amino, hydroxy and carbalkoxy groups, and R2 is selected from the class consisting of the hydrogen atom and alkyl, aralkyl, aryl, alicycllc and heterocyclic groups and, together with R1,

a divalent group linking the carbon atoms' to which R1 and R2 are attached, the quantity of such compound being between 0.02 g. to 1 g. per 1 /2 g. mols. silver halide in the emulsion.

3. A photographic gelatino silver iodobromide emulsion containing a small quantity of a compound of the general formula:

where R1 is selected from the class consist ing of alkyl, aryl, aralkyl, alicyclic, heterocyclic,

amino, hydroxy and carbalkoxy groups, and R2 is selected from the class consisting of the hy-- drogen atom and alkyl, aralkyl, aryl, alicyclic and heteroeyclic groups and, together with R1, a divalent group linking the carbon atoms to which R1 and R2 are attached, the quantity of such compound being between 0.02 g. to 1 g. per 1 g. mols. silver iodobromide in the emulsion.

DOUGLAS JAMES FRY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,449,225 Heimbach et a1. Sept. 14, 1948 2,476,536 Dersch July 19, 1949 

1. A PHOTOGRAPHIC GELATINO SILVER HALIDE EMULSION CONTAINING A SMALL QUANTITY OF A COMPOUND OF THE GENERAL FORMULA: 